WASHINGTON — Defense Secretary Robert Gates Thursday approved new rules that will make it harder to discharge gays from the military, calling the changes a matter of “common sense and common decency.”

Gates announced new guidelines for how the Pentagon carries out the 1993 law banning gays from serving openly in the military — rules which essentially put higher-ranking officers in charge of discharge proceedings and impose tougher requirements for evidence used against gays.

The new guidelines go into effect immediately. They are considered a stopgap measure until Congress decides whether to go along with President Barak Obama’s call for a repeal of the “don’t ask, don’t tell” law.

“I believe these changes represent an important improvement in the way the current law” is applied, Gates told a Pentagon news conference. He said the changes will provide “a greater measure of common sense and common decency” on a difficult issue.

The changes raise the level of officer authorized to initiate a fact-finding inquiry into a case, the level of officer who can conduct an inquiry and of the one that can authorize a dismissal.

To discourage the use of overheard statements or hearsay, from now on any evidence given in third-party outings must be given under oath, Gates said. Cases of third-party outings also have included instances in which male troops have turned in women who rejected their romantic advances or jilted partners in relationship have turned in a former lover.

Some kinds of confidential information also will no longer be allowed, including statements gays make to their lawyers, clergy, psychotherapists or medical professionals in the pursuit of health care.

The individual service branches will have 30 days to change their regulations to conform to the new rules.

Military officials, Republicans and even some conservative Democrats have been reluctant to embrace a change in the existing law. They say they support Gates’ review of the policy but that no changes should be made if they might undermine military cohesion and effectiveness.

Sen. Carl Levin, D-Mich., chairman of the Senate Armed Services Committee, and other Democrats say the time has come to repeal the ban and have called for an immediate moratorium on dismissals.

Nathaniel Frank, a senior research fellow with the Palm Center, which supports a repeal of the ban, said it is unclear how much of an impact the new guidelines would have because regulations already restrict third-party allegations.

“Anything that continues to allow the discharge of service members for something that research shows has no bearing on military effectiveness will not go far enough,” Frank said.

An estimated 13,000 have been discharged under the law. The Pentagon didn’t officially begin tallying discharges until a few years after the law was implemented, and official figures show roughly 11,000 discharged since 1997 with the peak in 2001 before the military became strained by the wars in Iraq and Afghanistan.